A lead storage battery for automobiles is widely used for starting an engine, and for supplying an electric power to electronic auto parts. In recent years, an idling stop system (which will be referred to as “ISS”, hereafter), which stops the engine when the vehicle temporarily stops, and restarts when the vehicle starts, is coming to be employed as a measure of environmental protection and a fuel consumption improvement. In a lead storage battery that is used in ISS, the number of times of discharging a large current when the engine starts increases because the start and the stop of the engine is frequently repeated, then, it combines with the use of the electronic auto parts to thereby cause discharge loads to become heavy.
The lead storage battery for automobiles is charged by an alternator with a constant-potential charging. In recent years, the set value of the alternator voltage is lowering for the purpose of suppressing the decrease of the electrolytic solution due to an electrolysis of water during charging. In recent years, in addition to the adoption of such a low charge voltage, the so-called power generation control system which is the method of “controlling the charge by the alternator during running according to the running state of vehicles and the charging state of the lead storage battery, to thereby reduce the engine load to aim at improvement in fuel consumption and CO2 reduction” is also adopted. In such a method, the lead storage battery is not easily charged and is therefore unlikely to become a fully charged state. On such a working condition, the lead storage battery becomes often used in a state of being not fully charged and being excessively discharged.
If the lead storage battery has not been completely charged and a state of low charging level is continued, there is a case where a phenomenon “sulfation” occurs, in which lead sulfate, which is an inactive discharge product, accumulates on a polar plate. It is known that in such a situation, an active material is not easily reduced (it is not easily charged), and that accordingly the battery performance such as the cycle characteristics is lowered.
In addition, when complete charging is not easily performed, a stratification phenomenon occurs, in which a difference in the concentration of dilute sulfuric acid, which is an electrolytic solution, arises between an upper part and a lower part of the polar plate in the lead storage battery. In this case, the concentration of dilute sulfuric acid becomes high in the lower part of the polar plate, and therefore, the sulfation occurs. Because of this, the reactivity at the lower part of the polar plate is lowered and only the upper part of the polar plate becomes to react intensively. As a result, a degradation progresses, for example, the connection between active materials becomes weak, and thus the active material in the upper part of the polar plate exfoliates from the current collector (for example, current collecting grid), which supports the active material, to thereby lower the battery performance such as the cycle characteristics.
In these circumstances, the following Patent Literature 1 discloses, as means for improving the cycle characteristics and the like, the technique concerning a negative electrode for the lead storage battery obtained with the use of a negative electrode active material, and a condensate of phenols, an aminobenzenesulfonic acid and formaldehyde.